You could accomplish guiding users as to the right choices regarding linear
vs perceptual by creating presets and allowing users the freedom to control
their own editing decisions. You don't have to build fences around what
people can do with their own RGB color data.

One design maxim is “Make common things easy, rare things possible.”.
If there is confidence that a default behavior covers more than
99.999% of uses, and there are intended ways of working around the
limitations - I think it might be of the benefit of both the normal
user and the deviating expert that likely also does not need to do it
in more than a couple of % of cases.
/Ø

Who decides what's common and what's rare for an artist to want to do?
The GIMP devs? Isn't that just a trifle presumptuous?

These kinds of decisions belong with the users, not the devs.

For instance, on what basis did you decide that drawing gradients should
always and only be done using perceptually uniform RGB? Back before all
the rendering software switched to a linearized workflow, a
radiometrically correct gradient was the poster child of why editing
should be done on linearized RGB data.

Don't use code to micromanage what users can do their own data based on
what devs think is "common" or "correct". Make it easy for the user to
choose between linear vs perceptual for ALL ops, and put in good presets.